The long-term objective of the proposed research is to identify the genes and to characterize the action of the gene products that control transcription and transcript termination in the Drosophila retrotransposon gypsy, considering it as a model system relevant to basic problems of retroviral expression. These objectives bear importantly on disease processes that result from the expression of retroviruses and retrotransposons and from alterations in their control. Examples of such alterations are the activation of proto-oncogenes by adjacent altered retrotransposons and the apparent involvement of cellular and/or viral genes in the activation of the human immunodeficiency virus HIV-1 from its latent state. The planned studies take advantage of the existence of a class of Drosophila cellular genes (allele-specific modifiers) that are promising candidates for regulators of the expression of retrotransposons. Mutations in such genes will be assayed for their effects on transcription and transcript termination in specially designed gypsy constructs. This will critically test preliminary indications that certain modifier genes affect the activity of the gypsy polyadenylation signals while others alter the strength of the gypsy promoter. Mutations in additional genes affecting transcript termination will be selected by the use of a white gene construct designed for the purpose. Protein binding sites will be mapped in the 98 bp minimal promoter region that lies between -38 and +60 in the gypsy long terminal repeat (LTR). Segments of this region that bind protein from nuclear extracts will be used as probes to isolate clones of the genes that code for the corresponding binding proteins from cDNA expression libraries. The effect of individual site-directed mutations on gypsy expression in transfected cells will be correlated by gel retardation analysis with their effects on the binding of each cloned protein, in order to determine whether the protein is functional. Following this combination of molecular and genetic approaches, the investigator hopes to arrive at a detailed picture of the regulatory circuits governing the expression of the gypsy retrotransposon.